The
motor theory of speech perception is the hypothesis that people
perceive spoken words by identifying the
vocal tract gestures with which they are pronounced rather than by identifying the
sound patterns that speech generates.
[1][2][3][4][5] It originally claimed that speech perception is done through a specialized
module that is
innate and human-specific. Though the idea of a module has been qualified in more recent versions of the theory,
[5] the idea remains that the role of the speech
motor system is not only to produce speech articulations but also to detect them.
The hypothesis has gained more interest outside the field of speech perception than inside. This has increased particularly since the discovery of mirror neurons that link the production and perception of motor movements, including those made by the vocal tract.[5] An alternative interpretation of research linking speech perception to speech production, however, is that it links to speech imitation rather than speech perception.[6]
The theory was initially proposed in the Haskins Laboratories in the 1950s by Alvin Liberman and Franklin S. Cooper, and developed further by Donald Shankweiler, Michael Studdert-Kennedy, Ignatius Mattingly, Carol Fowler and Douglas Whalen.
The hypothesis has its origins in research using pattern playback to create reading machines for the blind that would substitute sounds for orthographic letters.[7] This led to a close examination of how spoken sounds correspond to the acoustic spectrogram of them as a sequence of auditory sounds. This found that successive consonants and vowels overlap in time with one another (a phenomenon known as coarticulation).[8][9][10] This suggested that speech is not heard like an acoustic "alphabet" or "cipher," but as a "code" of overlapping speech gestures.
